This invention relates to a wind turbine augmented by a diffuser for driving a generator of electricity and, more particularly, to such a turbine wherein an element of the diffuser can be folded to reduce the size of the diffuser, and to limit charging by the generator under very high wind conditions.
A turbine converts the power of a moving fluid, such as the moving air in wind, to mechanical power in the rotating shaft of the turbine. As is well known, turbines are constructed with differing physical structures to produce a large or a small fluid pressure differential between the inlet and the outlet ports of the turbine. In a wind turbine the foregoing pressure differential is small, the ratio of the fluid pressure at the inlet and outlet ports of the turbine being near unity. The output shaft of the turbine is connected to a load which utilizes the power extracted from the moving fluid.
As an example of a wind turbine connected to a load, U.S. Pat. No. 4,075,500 which issued in the name of Oman et al on Feb. 21, 1978 shows a turbine having an electric generator. Historically, an early use for a wind turbine is the driving of mills, such as flour mills sawmills, or fulling mills; such well known and referred to as a windmill.
As seen in the aforementioned Oman patent, a turbine may be augmented by a diffuser. The diffuser is a duct or set of ducts that produces a deceleration of the moving fluid, such as the moving air, with a resultant increase in the fluid pressure. The combination of a diffuser with the turbine increases the effectiveness of the turbine by allowing it to extract more power from the air incident upon the turbine than would be obtained in the absence of the diffuser. For subsonic fluid flow, as obviously occurs in the case of a wind turbine, the diffuser takes the form of a diverging duct.
An electric generator, driven by a wind turbine serves as a source of electric power which may be utilized at remote sites where electric power may not normally be available. For example, in a sailboat moored, anchored or at a dock between usage periods, such a turbine driven generator may be deployed for recharging the batteries which power the radios, pumps, lights, and other electrical devices aboard the sailboat. Even though the turbine blades of such a portable turbine driven generator may well be substantially smaller than the turbine blades utilized in a fixed installation capable of a comparable power output, the augmentation of the diffuser provides a sufficient increase in the conversion from wind power to electric power to provide great utility to such a portable unit.
A problem arises in that the physical size of the diffuser, at its maximum diameter, is substantially larger than the turbine rotor with the result that the size of the diffuser limits the power output of a turbine constrained by the space available for storage. An additional problem inherent to all wind turbine must also be considered in the use of a diffuser. The problem occurs in the presence of excessively high winds wherein the high energy flow in the air is converted by the diffuser to still higher energy flow to the blades of the turbine. An electric generator driven by the turbine would then produce excessively high current resulting in a possible burn-out of the generator.